1. Field of the Invention
The present invention relates to a semiconductor device.
2. Background of the Related Art
In general, an intelligent power module (IPM) is a semiconductor device in which a power semiconductor element, a control circuit, a driving circuit, a protection circuit, and the like form a module. According to a conventional sensor technique for the IPM, a sense diode in which diodes are formed on a power semiconductor element is known. According to another sensor technique, a shunt resistor and a thermistor are provided in a power semiconductor module, a shunt resistor is used as a current sensor, and a thermistor is used as a temperature sensor. When a power semiconductor element operates, heat corresponding to the loss thereof is generated. The sensor technique detects the temperature of the power semiconductor element and controls a gate voltage and the like to protect the power semiconductor element so that the power semiconductor element does not malfunction due to this heat.
A sense diode detects the temperature of a power semiconductor element based on the temperature dependence of the current characteristics of the sense diode. Since silicon which is a conventional semiconductor element material has large current-temperature dependence, a sense diode formed from silicon can easily detect the temperature based on a change in current. On the other hand, a wide-bandgap semiconductor element such as a silicon carbide (SiC) which attracts attention as a next-generation semiconductor material has smaller current-temperature dependence than silicon. Thus, when a sense diode is manufactured using the same material as the wide-bandgap semiconductor element, it is difficult to obtain sufficient accuracy. Moreover, when a sense diode is manufactured using a silicon semiconductor by a step separate from the step of manufacturing the wide-bandgap semiconductor element, the number of manufacturing steps may increase.
A shunt resistor and a thermistor are generally formed at a position different from a power semiconductor element on an insulating circuit substrate within the power semiconductor module. Thus, the use of a shunt resistor and a thermistor can become the cause of an increase in external size of the power semiconductor module. Moreover, since the shunt resistor and the thermistor are separated from the power semiconductor element, the response speed for temperature detection is not always fast. Due to this, it is sometimes difficult to obtain sufficient characteristics required for sensors used for a protection circuit and a control circuit.
Moreover, a method of calculating a junction temperature of a SiC gate turn-off thyristor (GTO) which is a semiconductor switching element by utilizing the fact that a storage time TS as a turn-off characteristic time of the SiC GTO has large temperature dependence is known as a method of measuring the temperature of a semiconductor device, see Japanese Patent Application Publication No. 2007-93335 (Patent Literature 1). However, this method relates to GTOs and it is difficult to apply the method to measurement of the temperature of other semiconductor elements such as a metal-oxide semiconductor field-effect transistor (MOSFET).
Moreover, a silicon carbide semiconductor device having a diode (Schottky barrier diode (SBD)) for measuring the temperature of a silicon carbide semiconductor element is known. In this device, an anode voltage corresponding to a setting temperature at which a control IC has to stop a MOSFET is calculated by examining current-voltage characteristics of the SBD. Moreover, the MOSFET is protected from being overheated by setting the anode voltage to the calculated voltage, see WO 2012/086099 (Patent Literature 2). However, this device could not be applied to a semiconductor device which does not have a SBD.
Further, a SiC semiconductor device in which a temperature-detecting resistor is formed using a portion of a barrier metal formed on a bottom surface of a semiconductor element and the temperature of a SiC semiconductor is detected using the fact that a resistance value of the temperature-detecting resistor changes depending on temperature is known, see Japanese Patent Application Publication No. 2013-26563 (Patent Literature 3). However, when temperature is measured using the temperature-detecting resistor, it is necessary for the temperature-detecting resistor to have a large length in order to obtain an output voltage of a certain magnitude. Thus, a region in which the temperature-detecting resistor is to be provided is limited.
Further, an apparatus for measuring the temperature of a semiconductor substrate is known. In this apparatus, light from a light source strikes the semiconductor substrate and light scattered from the semiconductor substrate is received and dispersed to obtain the optical spectrum thereof. The temperature of the semiconductor substrate is calculated and measured based on the optical spectrum, see Japanese Patent Application Publication No. 2010-25756 (Patent Literature 4). However, this apparatus is a temperature measuring apparatus for a semiconductor substrate which is a material of a semiconductor device and is not an apparatus for measuring the temperature of a semiconductor device in operation.
An object of the present invention is to provide a semiconductor device which has a wide-bandgap semiconductor element such as a SiC and which includes a sensor having sufficient characteristics required for protecting and controlling the semiconductor element.